Linear compressor unit

ABSTRACT

A linear compressor unit including a reciprocating magnet driven by an electromagnetic alternating field. The magnet drives a piston reciprocatingly in a cylinder in a module casing, which casing also encloses a buffer volume. The cylinder is mounted in the casing so that it can oscillate. The cylinder includes an inlet opening coupled to an inlet passage in the module casing lying opposite to one another but without making contact with each other and forming a passage to the buffer volume. At least one restrictor element is located in the passage to dampen sound of the unit.

The invention relates to a linear compressor unit which can especiallybe used to compress a coolant in a refrigerating device such as arefrigerator, a freezer or the like.

Reciprocating-piston compressors driven by rotary motors areconventionally used in domestic refrigerating devices. For domesticusage it is very important that these compressors only generate minimalrunning noise. An important source of this noise is the intermittentsuction of the coolant to be compressed, caused by the forward andbackward movement of the piston. This intermittent suction causespulsations which must be reduced by corresponding damping devices. Acommon design principle for this purpose is to pass the flow of gaseouscoolant via chambers which are constructed, for example, as Helmholtzresonators or the like, so that the pulsations are strongly damped anddo not reach the outside. These chambers are usually built directly ontothe pump of the compressor. This pump is enclosed in a module casing fornoise damping and insulation. Between the inlet of the chambers and themodule casing of the compressor, there is a small spacing which allowsthe passage of coolant into the buffer volume of the casing modulesurrounding the pump.

Recently, so-called linear compressors have been developed whichdispense with a rotary motor to drive the compressor piston and insteadof this, drive this piston directly by a magnet which can be driven tomove linearly back and forth in an alternating electromagnetic field. Asa result of this driving principle, the cylinder in a linear compressoris subject to strong vibrations excited by the forward and backwardmovement of the magnet and the piston coupled thereto.

If an attempt is made to apply the construction principle known from thebuilding of rotary-motor-driven compressors, as a result of which aninlet opening of the cylinder and an inlet passage of the module casingcontaining the cylinder lie opposite one another without making contact,forming a passage to the buffer volume, to the building of linearcompressor units, the problem arises that the unavoidable oscillatorymovement of the linear compressor unit modulates the cross-section ofthe passage to the buffer volume at the resonance frequency of themovable piston and in this way, tends to increase the noise productionrather than dampen it.

The object of the present invention is to provide a linear compressorunit with an encapsulated cylinder in which the generation of noise bymodulation of the passage cross-section to the buffer volume iseffectively limited.

The object is solved by a linear compressor unit having the feature ofclaim 1. The restrictor element in the passage prevents the excitationof resonances in the buffer volume and therefore excessive noise.

The restrictor element is preferably formed by walls which are attachedto the module casing or to the cylinder and which intermesh. The wallscan have an arbitrary suitable shape in order to bring about a pressuredrop in gas flowing back and forth between the inlet opening and thebuffer volume as a result of friction at said walls. Walls whichsurround the inlet opening or the inlet passage in a ring shape orconcentrically are preferable.

The cylinder itself preferably has one or a plurality of sound-dampingchambers between its inlet opening and a working chamber which receivesthe piston. Thus, intensive pressure thrusts produced by the piston inthe working chamber are partly intercepted before they reach the passageto the buffer volume.

A further appropriate sound-damping measure is to insert, in the inletpassage of the module casing, a sound-damping chamber through which themedium to be compressed flows. This chamber can be attached directly tothe wall of the module casing and have a flat cylindrical shape throughwhich the inlet passage runs along the cylinder axis of the chamber.

The oscillatory holder of the cylinder is preferably formed by an outletpipe through which the compressed medium leaves the cylinder. The outletpipe is preferably guided helically around the cylinder chamber. Themagnet which drives the forward and backward movement of the piston canespecially be arranged in an axial extension of the piston or around thepiston in a ring shape.

Further features and advantages of the invention are obtained from thefollowing description of exemplary examples with reference to theappended figures. In the figures:

FIG. 1 is a schematic partial section through a first embodiment of thelinear compressor unit according to the invention;

FIG. 2 is a detailed section through the head region of the linearcompressor unit from FIG. 1;

FIG. 3 is a section through a second embodiment of the linear compressorunit.

The linear compressor unit shown in FIG. 1 comprises a hermeticallysealed metal module casing 1, which accommodates a pumping section 2 anda driving section 3 of the compressor unit. The driving section 03 shownin cross-section substantially comprises a bar-shaped permanent magnet4, which is arranged in the interior cavity of a coil 5 such that it canbe moved in the longitudinal direction. A restoring spring 6, in thiscase in the form of a helical spring, presses the magnet 4 in thedirection of the pumping section 2. As a result of an alternatingcurrent applied to the coil 5, an alternating magnetic field can begenerated in its interior which excites the magnet 4 to move back andforth along the axis of the coil 5.

Fixedly mounted on the magnet 4 is a piston 7 which engages in a workingchamber 8 of a cylinder 9 and can be displaced therein by the movementof the magnet. On a wall of the working chamber 8 located opposite tothe piston 7 two openings are each provided with a valve 10, 11. Thevalves 10,11 are shown here as flap or blade valves but it is understoodthat any type of valve which only allows medium to flow in onedirection—into the working chamber 8 in the case of the valve 10 and outof said working chamber in the case of the valve 11—can be used.

Medium to be compressed reaches the working chamber 8 via an inletpassage 12 in the form of a pipe section which crosses the module casing1 and is fixedly anchored therein, an inlet opening 13 of the cylinder 9and a sequence of chambers 14, 15, 16 which are mounted in the case ofthe cylinder 9 before the working chamber 8.

The inlet opening 13 of the cylinder 9 is located at the end of a pipeconnecting piece 17 which is located at a distance from a front wall ofthe cylinder 9 in a direction parallel to the direction of movement ofthe magnet 4 and the piston 7. This pipe connecting piece 17 lies inalignment opposite to a second pipe connecting piece 18 which forms theportion of the inlet passage 12 engaging into the interior of the modulecasing 1.

The pipe connecting piece 18 carries a radially distant flange 19 onwhich a plurality of cylindrical walls 20 are arranged concentrically tothe longitudinal axis of the inlet passage 12. Corresponding walls 21with suitably staggered diameters are attached to the front side of thecylinder 9 and engage in each case between two of the walls 20.

Compressed medium leaves the working chamber 8 via an outlet pipe 22which is affixed at one end to the cylinder 9, runs helically around thecylinder 9 and finally crosses through the wall of the module casing 1.This outlet pipe 22 at the same time forms a suspension of the cylinder9 in the module casing 1 which allows oscillating movements of thecylinder 9, especially in the longitudinal direction.

During operation of the compressor unit, with every movement of thepiston 7 to the left in the figure, medium contained in the workingchamber 8 is compressed and escapes through the outlet valve 11 as soonas the pressure in the working chamber 8 exceeds that in the outlet pipe22. In this case, the piston 7 exerts a pressure directed towards theleft in the figure on the cylinder 9, to which the cylinder can yield alittle as a result of its elastic suspension. During this movement ofthe piston 7 the walls 20 and 21 are displaced towards one another and agap between the end of the pipe connecting piece 18 and the inletopening 13 of the cylinder 9 becomes narrower. As a result of thismobility, the transfer of the loud knocking noises which the piston 7causes at its left reversal point, to the module casing 1 and thus intothe surroundings of the compressor unit is avoided.

When the piston 7 is pulled to the right by the magnet 4 and the workingchamber 8 becomes larger again, an underpressure is formed therein whichon the one hand results in fresh medium being sucked in via the inletpassage 12 and on the other hand results in the cylinder 9 following thepiston 7 a little far to the right. The broadening of the gap 23resulting therefrom is not so large however that the walls 20, 21 comeout of engagement as a result. The intermeshing walls 20, 21 thus act asa restrictor element which damps the outflow of medium from the buffervolume 24 into the working chamber 8 during the expansion phase of theworking chamber 8 and correspondingly damps an inflow of the medium backinto the buffer volume 24 via the inlet passage 12 in the compressionphase of the working chamber 8. Thus, even when the working frequency ofthe linear compressor unit, i.e. the oscillation frequency of the magnet4, coincides with the resonance frequency of the buffer volume 24,pressure oscillations of the buffer volume 24 are effectively damped andtheir amplitude is kept small. Thus, one of the components whichcontributes to the operating noise of a linear compressor unit iseffectively suppressed.

The chambers 14, 15, 16 of the cylinder 9 likewise have sound-dampingfunctions. They are executed in a fashion known per se from sounddamping technology as Helmholtz resonators.

As a further measure to damp the operating noise of the compressor unit,a further sound-damping chamber 25 is inserted in the inlet passage 12of the module casing 1. This chamber 25 of which one wall is formed bythe module casing 1 itself, has a flat-cylindrical form wherein theinlet passage 12 crosses the chamber 25 along its cylinder axis. Thechamber 25 also acts a Helmholtz resonator with an inlet opening whichextends over the entire circumference of the inlet passage 12 and isthus particularly effective.

FIG. 3 shows a second embodiment of the linear compressor unit whichdiffers from that in FIG. 1 by the design of its driving section 3. Thepumping sections 2 of both embodiments are identical. Whereas in theembodiment in FIG. 1, the permanent magnet 4 is arranged in an axialextension of the piston 7, in the case shown in FIG. 3 it surrounds thepiston 7 in a ring shape and is fixedly connected thereto by a flange 28or individual radially oriented supporting arms. This annular magnet 4is surrounded externally by a coil 5 which can excite it to oscillate asa result of an alternating magnetic field. Effective coupling of themagnetic field of the coil to the magnet 4 is provided by twosheet-metal packings 26, 27 which are each arranged in an annularintermediate space between the magnet and the cylinder, maintaining asmall air gap towards the magnet 4, or externally surrounding the magnet4 and the coil 5 in a ring shape.

1. A linear compressor unit, comprising: an electromagnetic alternatingfield surrounding at least a portion of a cylinder; a magnet located insaid electromagnetic alternating field in said cylinder, said magnetdisplaceable back and forth in said electromagnetic alternating field; apiston located in said electromagnetic alternating field in saidcylinder drivingly connected to said magnet; a buffer volume; a modulecasing which encloses said cylinder and said buffer volume; saidcylinder mounted in said module casing so that said cylinder canoscillate in said module casing; said module casing including an inletpassage for media to be compressed; said cylinder including an inletopening lying opposite said inlet passage without making contacttherewith; a passage to said buffer volume formed between said inletopening and said inlet passage; and at least one sound restrictorelement located in said buffer volume passage, said sound restrictorelement including a plurality of generally cylindrical walls, with afirst group of walls attached to said module casing and a second groupof walls attached to said cylinder for generally reciprocal relativemotion between said first group of walls and said second group of wallswith said first group of walls being intermeshed with said second groupof walls, said first group of walls and said second group of wallsforming a pathway, the pathway having a first run and a second run, thefirst run of the pathway extending from said passage to said buffervolume to a first change of direction portion communicating the firstrun with the second run with one surface of said first group of wallsdelimiting one side of the first run of the pathway and one surface ofsaid second group of walls delimiting an opposite side of the first runof the pathway and the second run extending from the first change ofdirection portion to a second change of direction portion with anothersurface of said first group of walls delimiting one side of the secondrun of the pathway and another surface of said second group of wallsdelimiting an opposite side of the second run of the pathway, thepathway guiding media to be compressed that enters the pathway via saidpassage, moves in a first direction along the first run of the pathway,undergoes a change in direction while passing through the first changeof direction portion, moves in a second direction along the second runof the pathway, and thereafter undergoes another change in directionwhile passing through the second change of direction portion.
 2. Thelinear compressor unit according to claim 1, including said intermeshingwalls are formed in a ring shape and surround at least one of said inletopening and said inlet passage.
 3. The linear compressor unit accordingto claim 1, including said cylinder including a chamber for receivingsaid piston and at least one sound-dampening chamber through which saidmedium to be compressed flows, said sound-dampening chamber arrangedbetween said inlet opening of said chamber and said piston chamber. 4.The linear compressor unit according to claim 1, including at least onesound-dampening chamber through which said medium to be compressed flowslocated in said inlet passage of said module casing.
 5. The linearcompressor unit according to claim 4, including said sound-dampeningchamber is formed in a flat-cylindrical shape with a cylindrical axisopening and said inlet passage of said module casing is substantiallyaligned therewith.
 6. The linear compressor unit according to claim 1,said cylinder mounted for oscillation in said module casing by acylinder outlet pipe.
 7. The linear compressor unit according to claim6, including said outlet pipe is formed helically around said cylinder.8. The linear compressor unit according to claim 1, including saidmagnet is formed as an axial extension of said piston.
 9. The linearcompressor unit according to claim 1, including said magnet is formed asa ring shaped body at least partially surrounding said piston andconnected thereto at one end of said piston.
 10. The linear compressorunit according to claim 1, said cylinder mounted for oscillation in saidmodule casing by a cylinder outlet pipe formed helically around saidcylinder.